In general, a check valve means a valve assembly configured to control a fluid flow only in one direction. The check valve permits a fluid to flow in a first direction, but controls the fluid so that it does not flow in a second direction opposite the first direction. Various structures using a ball or elastic plate have been known as an internal structure for permitting a flow of a fluid only in one direction.
Furthermore, it is impossible for such a conventional check valve to control a flow of a fluid in an opposite direction because the flow direction of the fluid has been determined. That is, if the check valve is installed so that a fluid flows only in a first direction when it is installed in a pipe, the fluid cannot flow in a second direction opposite the second direction in the state in which the check valve has been installed. Accordingly, in order for the fluid to flow in the second direction opposite the first direction, an existing valve must be replaced. Accordingly, the conventional check valve has a disadvantage in that a user cannot control the flow direction of a fluid in a required direction.